Evidence for a stem-cell lineage in corneal squamous cell carcinoma using synchrotron-based Fourier-transform infrared microspectroscopy and multivariate analysis

The cornea is one of the few human tissues where the in situ locations of stem cells (SCs), transient-amplifying (TA) cells and terminally-differentiated (TD) cells have been relatively well localised and characterised. Mid-infrared (IR) (4000-400 cm(-1)) is absorbed by biological molecules and facilitates the acquisition in the biochemical-cell fingerprint region (1800-900 cm(-1)) of spectra representative of structure and function. Human cornea derived from normal or squamous cell carcinoma (SCC) samples were acquired, cryosectioned (10 mu m), floated onto BaF2 windows and interrogated using synchrotron-based radiation (SRS) Fourier-transform IR (FTIR) microspectroscopy. Spectra were analysed using principal component analysis (PCA) with or without linear discriminant analysis (LDA) to allow cluster analysis of the cell categories. A clear cell lineage emanating from SCs to TA cells to TD cells was noted in normal samples. Within the SCC samples, a small sub-population of the cell-derived spectra pointed to a SC-like phenotype with the vast majority pointing to a TA cell-like character; these cells would tend to be the most proliferative within a tissue. Our findings suggest that SRS FTIR microspectroscopy has the potential to identify and characterise cancer SCs